# Question #6f0e8

May 14, 2016

One equivalent is usually defined as the amount of substance reacted or produced in a red-ox reaction by the transfer of one mole of electrons.

#### Explanation:

Combustion of methane with oxygen is a convenient example. First write the balanced reaction:

$C {H}_{4} + 2 {O}_{2} \to C {O}_{2} + 2 {H}_{2} O$

The oxidation state of the carbon atom goes from -4 to +4, and each of the 4 oxygen atoms goes from 0 to -2, so 8 electrons are transferred in this reaction. It may help to think about this by rewriting the reaction to correspond to 1 mole of electrons transferred:

$\frac{1}{8} C {H}_{4} + \frac{1}{4} {O}_{2} \to \frac{1}{8} C {O}_{2} + \frac{1}{4} {H}_{2} O$

Now it is easy to see that 1/8 mol of methane reacts per mole of electrons. The molar mass of methane is 16 g, so the mass equivalent of methane is $16 g \cdot \frac{1}{8} = 2$ g

Similarly, the mass equivalent of ${H}_{2} O$ produced is
$18 g \cdot \frac{1}{4} = 4.5 g$